obviously the same genetics, perhaps a similar environment. but they were able to much better control that. and when they looked at those sibling studies, that's when some of these differences really emerged. >> so the bottom line, if you're a guy over the age of 40 years old and you're considering having a child or if you've had one over the age of 40, what do you need to know? >> well, look, first of all the likelihood is it's not going to have any of these things that we talk about whether it's autism, bipolar disorder, even though the increased likelihood is there. the risk is still pretty small. >> so the majority of dad over 40 will not have any of these things. >> yeah. and i think that's the good news. i'm a bit of an older dad myself. so i pay attention to these sorts of studies. but the idea that it will affect any given individual is still pretty small. what i would say from a cultural standpoint we talk a lot about the fact that women in advanced maternal age has become more common, advanced paternal age has become more common as w